The usual two bed regenerative fume incinerator, or regenerative thermal oxidizer, has two ceramic filled beds, a combustion zone operating at about 1600 degrees F. and valving at the cold ends of the beds to switch the gas flow direction through the beds every minute or so. Unfortunately, when the beds are switched, the bed which was receiving impure gas containing oxygen and volatile organic compounds, suddenly becomes the exit bed and a surge of impure air leaves the incinerator.
Several expensive methods of handling the surge of impurities, which occurs upon switching flow through the ceramic beds, have heretofore been proposed. U.S. Pat. No. 3,3870,474 teaches the use of a third bed so that a bed can be purged clean before it is put back in operation, and also teaches the use of an empty vessel to receive the surge and slowly feed the surge gases back to a receiving bed. Both of these teachings require the use of a bed or vessel about the size of the regenerative beds. The system shown in U.S. Pat. No. 5,184,951, purges the dirty bed while bypassing the impure feed directly to the combustion chamber. The bypassing results in a large thermal loss. U.S. Pat. No. 5,145,363 teaches discharge from the combustion chamber to the exhaust stack while the dirty bed is purged. This also results in a large thermal loss.